The delivery of radio frequency (RF) energy to target regions within solid tissue is known for a variety of purposes of particular interest to the present invention. In one particular application, RF energy may be delivered to diseased regions (e.g., tumors) for the purpose of ablating predictable volumes of tissue with minimal patient trauma.
RF ablation of tumors is currently performed using one of two core technologies. The first technology uses a single needle electrode, which when attached to a RF generator, emits RF energy from an exposed, uninsulated portion of the electrode. The second technology utilizes multiple needle electrodes, which have been designed for the treatment and necrosis of tumors in the liver and other solid tissues. U.S. Pat. No. 6,379,353 discloses such a probe, referred to as a LeVeen Needle Electrode™, which comprises a cannula and an electrode deployment member reciprocatably mounted within the delivery cannula to alternately deploy an electrode array from the cannula and retract the electrode array within the cannula. Using either of the two technologies, the energy that is conveyed from the electrode(s) translates into ion agitation, which is converted into heat and induces cellular death via coagulation necrosis. The ablation probes of both technologies are typically designed to be percutaneously introduced into a patient in order to ablate the target tissue.
Because the size of tissue coagulation created from a single electrode, and to a lesser extent a multiple electrode array, has been limited by heat dispersion, it is known to introduce an electrically conductive fluid, such as saline, into targeted tissue to increase the tissue conductivity, thereby creating a larger lesion size. It has been shown that the introduction of saline into targeted tissue during an ablation procedure increases the tissue conductivity, thereby creating a larger lesion size. Saline can be introduced into the tissue using a separate device, such as a syringe, or can be perfused from the ablation probe itself.
When designing RF ablation probes using either of the two technologies, RF energy is often delivered to the distal electrode(s) via the shaft itself, thereby requiring the probe to be electrically insulated to prevent undesirable ablation of healthy tissue. In the case of a single needle electrode, all by the distal tip of the electrode is coated with an electrically insulative material in order to focus the RF energy at the target tissue located adjacent the distal tip. In the case of a LeVeen Needle Electrode™, RF energy is conveyed to the needle electrodes through the inner electrode deployment member, and the outer cannula is coated with the electrically insulative material to prevent RF energy from being transversely conveyed from the inner electrode deployment member along the length of the probe. When designing RF ablation probes, it is also desirable to make the profile of the probe shaft as small as possible in order to minimize any pain and tissue trauma resulting from the percutaneous insertion of the probe into the patient to be treated. Thus, it is advantageous that the electrically insulative material applied to the probes be as thin as possible. However, RF ablation probes are often introduced through other tightly toleranced devices that may compromise the integrity of the thinly layered insulation, thereby inadvertently exposing healthy tissue to RF energy.
For example, probe guides are often used to point ablation probes towards the target tissue within a patient. A typical probe guide takes the form of a rigid cylindrical shaft (about 1-2 inches in length) that is affixed relative to and outside of a patient, and includes a lumen through which the ablation probe is delivered to the target tissue. To maximize the accuracy of the probe alignment, it is desirable that the guide lumen through which the probe is introduced be about the same size as the outer diameter of the probe, thereby creating a tight tolerance between the probe and the probe guide. As another example, ablation probes are also often used with co-access assemblies that allow several different devices, such as ablation probes, biopsy stylets, and drug delivery devices, to be serially exchanged through a single delivery cannula. To minimize pain and tissue trauma, it is desirable that the profile of the delivery cannula be as small as possible. As a result, the lumen of the delivery cannula will typically be the same size as the outer diameter of the ablation probe, thereby creating a tight tolerance between the probe and the delivery cannula.
Thus, during the initial introduction of the probe through a delivery device, such as a probe guide or cannula of a co-access system, it is possible for the proximal edge of the probe guide to catch the distal edge of the insulation that coats the probe. If this occurs, a portion of the insulation may shear off as the probe is introduced through the delivery device. As a result, the attending physician will either have to replace the probe with a new one or risk ablating healthy tissue.
In addition, as discussed above, it is often desirable to deliver an electrically conductive fluid to the target tissue to facilitate the tissue ablation process. In the case where a co-access assembly is used, it has been proposed that the electrically conductive fluid could be introduced through either the co-access cannula or the ablation probe. However, equipping the cannula with lumens will ultimately increase its profile, thereby increasing the pain and tissue trauma associated with the percutaneous introduction of the cannula into the patient. It may be possible to equip the ablation probe with lumens. However, in the case of LeVeen Needle Electrodes™, every diminutive amount of space inside the cannula of the RF probe must be utilized by the needle electrodes, and therefore, it is difficult to design lumens within such probes.
There, thus, is a need for an improved ablation probe that minimizes the chance of inadvertent ablation of healthy tissue caused by the shearing of electrical insulation and/or an ablation probe that facilitates the delivery of an electrically conductive fluid when combined in a co-access ablation assembly.